Efficient thin curved eyepiece for see-through head wearable display

ABSTRACT

An eyepiece for a head wearable display includes a curved lightguide component, an input coupler, and an output coupler. The curved lightguide component guides display light received at an input region peripherally located from a viewing region and emits the display light along an eye-ward direction in the viewing region. The curved lightguide component includes an eye-ward facing surface that is concave and a world facing surface that is convex. The input coupler is disposed at the input region to couple the display light into the curved lightguide component. The output coupler is disposed at the viewing region to redirect the display light towards the eye-ward direction for output from the curved lightguide component. The output coupler is partially transmissive to ambient light incident through the world facing surface. The display light is guided between the input coupler and the output coupler entirely by total internal reflection.

TECHNICAL FIELD

This disclosure relates generally to the field of optics, and in particular but not exclusively, relates to eyepieces for head wearable displays.

BACKGROUND INFORMATION

A head mounted display (“HMD”) or head wearable display is a display device worn on or about the head. HMDs usually incorporate some sort of near-to-eye optical system to create a magnified virtual image placed a few meters in front of the user. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs display only a computer generated image (“CGI”), while other types of HMDs are capable of superimposing CGI over a real-world view. This latter type of HMD typically includes some form of see-through eyepiece and can serve as the hardware platform for realizing augmented reality. With augmented reality the viewer's image of the world is augmented with an overlaying CGI, also referred to as a heads-up display (“HUD”).

HMDs have numerous practical and leisure applications. Aerospace applications permit a pilot to see vital flight control information without taking their eye off the flight path. Public safety applications include tactical displays of maps and thermal imaging. Other application fields include video games, transportation, and telecommunications. There is certain to be new found practical and leisure applications as the technology evolves; however, many of these applications are limited due to the cost, size, weight, field of view, and efficiency of conventional optical systems used to implemented existing HMDs.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described.

FIG. 1 illustrates an eyepiece for a head wearable display, in accordance with an embodiment of the disclosure.

FIG. 2 illustrates how the eyepiece stitches together ray bundles output from a single display pixel to extend the eyebox of the eyepiece, in accordance with an embodiment of the disclosure.

FIGS. 3A and 3B illustrate a demonstrative monocular head wearable display including a see-through eyepiece, in accordance with an embodiment of the disclosure.

FIG. 4 illustrates a demonstrative binocular head wearable display including see-through eyepieces, in accordance with an embodiment of the disclosure.

FIG. 5 illustrates an example see-through add-on component for attaching to the curved lightguide component of the eyepiece, in accordance with an embodiment of the disclosure.

FIGS. 6A-6D illustrate various examples of input couplers and output couplers, in accordance with embodiments of the disclosure.

DETAILED DESCRIPTION

Embodiments of a system and apparatus for an eyepiece of a head wearable display that leverages total internal reflections between input and output couplers are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

FIG. 1 illustrates an eyepiece 100 for use with a head wearable display, in accordance with an embodiment of the disclosure. The illustrated embodiment of eyepiece 100 includes a curved lightguide component 105, a see-through add-on component 110, an input coupler 115 disposed at an input region 120, and an output coupler 125 disposed at a viewing region 130. The illustrated embodiment of curved lightguide component 105 includes an eye-ward facing surface 135 and a world facing surface 140.

Eyepiece 100 is well suited for use with head wearable display (“HMDs”). When integrated with an HMD, eyepiece 100 receives display light 145 generated by display source 150 at input region 120 peripherally located from viewing region 130 and emits display light 145 along an eye-ward direction in viewing region 130 toward a user's eye 155. Between input coupler 115 and output coupler 125 display light is guided entirely by total internal reflection (“TIR”) between eye-ward facing surface 135 and world facing curve 140.

In the illustrated embodiment, an optical combiner 160 may be integrated with an HMD to combine display light 145 with infrared (“IR”) light 165 along a common path through eyepiece 100. For example, infrared light 165 received from eyepiece 100 is directed by optical combiner to a camera 170, which may be configured to capture IR light 165 to monitor motion of eye 155. Correspondingly, optical combiner 160 directs display light 145 received from display source 150 towards eyepiece 100 for in-coupling into curved lightguide component 105 at input region 120. The illustrated embodiment of optical combiner 160 includes a minor 175 and a wavelength selective reflector 180. Minor 175 may be implemented as a conventional 100% reflective surface for reflecting the visible spectrum display light 145 while wavelength selective reflector 180 may be implemented as a “cold minor,” which substantially passes IR spectrum light 165 while substantially reflecting visible spectrum display light 145. In one embodiment, wavelength selective reflector 180 may be implemented using a multi-layer dichroic coating. Other optical combiner configurations may be implemented to multiplex IR light 165 and display light 145. Although not illustrated, an infrared emitter may be positioned to illuminate eye 155 with IR light 165.

In the illustrated embodiment, display light 150 is incident through eye-ward facing surface 135 at input region 120 and enters into curved lightguide component 105. Input coupler 115 is disposed at input region 120 and functions to redirect display light 145 along a trajectory within curved lightguide component 105 that causes TIR propagation down curved lightguide component 105 toward viewing region 130 and output coupler 125. In one embodiment, input coupler 115 is a mirror (e.g. silver coating or other reflective coating) having a freeform surface. Display light 145 is guided entirely via TIR from input coupler 115 to output coupler 125 where display light 145 is redirected out curved light guide component 105 via a final reflection off output coupler 125 at viewing region 130.

Output coupler 125 is a partial reflector or beam splitter (e.g., thin silver coating) having a freeform surface. In one embodiment, output coupler 125 is more transmissive to visible light than it is reflective. For example, output coupler 125 may be implemented as 15% reflective and 85% transmissive. Of course, other reflective/transmissive ratios may be implemented. Accordingly, viewing region 130 is partially transmissive to ambient light 185 incident through world facing surface 140 such that viewing region 130 is see-through. See-through add-on component 110 is disposed across viewing region 130 to provide a complementary curvature along world facing surface 140 to offset the optical power of the curvature of eye-ward facing surface 135 encountered by ambient light 185. In one embodiment, see-through add-on component 110 and curved lightguide component 105 are fabricated of the same transparent materials or transparent materials having substantially the same index of refraction. Thus, eyepiece 100 operates as an optical combiner, which combines ambient light 185 with display light 145 emitted out viewing region 130 along an eye-ward direction into eye 155. In this way, eyepiece 100 is capable of displaying an augmented reality to eye 155.

In the illustrated embodiment, see-through add-on component 110 is bonded to curved lightguide component 105 along an interface having output coupler 125 disposed there between. As mentioned above, world facing surface 140 and eye-ward facing surface 135 have complementary curvatures that substantially offset each other's optical power to ambient light 185 passing through. In other words, the input angle of ambient scene light entering world facing surface 140 is substantially equivalent to the output angle of ambient scene light exiting eye-ward facing surface 135. As such, eyepiece 100 passes at least a portion of ambient light 185 through viewing region 130 substantially without lensing, thereby permitting the user to have a substantially undistorted view of the ambient environment in front of eyepiece 100. In other embodiments, world facing surface 140 and eye-ward facing surface 135 are surfaces with non-complementary curvatures that collectively provide corrective lensing power to passing ambient light. Furthermore, by matching the refractive index of curved lightguide component 105 and see-through add-on component 110, there is no optical power at the curved interface of output coupler 125 for ambient light 185 passing through. However, the curvature of output coupler 125 does apply reflective lensing power to the internal display light 145.

Eyepiece 100 can be implemented as a thin, curved eyepiece having a thickness less than 4 mm. In one embodiment, curved lightguide component 105 has a thickness of about 3.5 mm when fabricated of a transparent material (e.g., OKP4HT-L, EP5000, polycarbonate, etc.) having an index of refraction of 1.64. The higher the refractive index the thinner the eyepiece. The curvatures of both eye-ward facing surface 135 and world facing surface 140 may be implemented as spherical surfaces. Collectively, the curvature and slim nature of eyepiece 100 provide a desirable industrial design. Eyepiece 100 not only has desirable industrial design, but is also efficient since the only lossy bounce for display light 145 traveling from input region 120 to viewing region 130 is the single redirection by output coupler 125. This permits output coupler 125 to be substantially more transmissive than reflective thereby improving the see-through characteristic of eyepiece 100 in viewing region 130.

In one embodiment, spherical curvatures for eye-ward facing surface 135 and world facing surface 140 along with freeform surfaces for input coupler 115 and output coupler 125 generate an implementation of eyepiece 100 that provides 15 degree field of view (“FOV”) and a 4.6 mm diameter unvignetted pupil when curved light guide component 105 is fabricated of a transparent material having a refractive index of 1.64. In this example embodiment, eye-ward facing surface 135 and world facing surface 140 having spherical radii of 90 mm and 93.5 mm, respectively. In this example, the freeform surfaces of input coupler 115 and output coupler 125 are defined by the following equations:

$\begin{matrix} {{z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {\sum_{j = 2}^{66}{C_{j}x^{m}y^{n}}}}},} & \left( {{Equation}\mspace{14mu} 1} \right) \\ {j = {\frac{\left( {m + n} \right)^{2} + m + {3n}}{2} + 1.}} & \left( {{Equation}\mspace{14mu} 2} \right) \end{matrix}$

In one embodiment, input coupler 115 has a freeform shape defined by equations 1 and 2 with coefficient values of x²=−3.0598E-03, y²=4.6107E-04, x³=3.3378E-05, x²y=4.8220E-06, (x,y,z)=(−28.5, 0, −3), and a relative tilt of 48.8 degrees. In one embodiment, output coupler 125 has a freeform shape defined by equations 1 and 2 with coefficient values of x²=4.6482E-03, y²=5.6526E-03, and a relative tilt of 26 degrees. Of course, other coefficient terms and/or values and dimensions may be implemented.

Eyepiece 100 may be combined with various other eyewear features. For example, world facing surface 140 may have a non-complementary curvature to eye-ward facing surface 135 to introduce prescriptive lensing to ambient light. In yet other embodiments, photochromic and/or electrochromic coatings may be applied to world facing surface 140 to provide a bright light shading feature (e.g., sunglasses).

FIG. 2 illustrates how eyepiece 100 stitches ray bundles output from a single display pixel to extend an eyebox of eyepiece 100, in accordance with an embodiment of the disclosure. Ray bundles 205 and 210 output from a single display pixel 215 are stitched together in the viewing region to extend eyebox 220 from which eye 155 can perceive display pixel 215. This stitching is achieved by leveraging the different paths followed by ray bundles 205 and 210. In fact, ray bundle 205 follows a path through curved lightguide component 105 having a different number of TIR reflections/bounces than ray bundle 210. For example, in the illustrated embodiment, ray bundle 205 encounters seven total reflections (including five TIR reflections off of eye-ward and world facing surfaces 135, 140) while ray bundle 210 encounters nine total reflections (including seven TIR reflections off of eye-ward and world facing surfaces 135, 140).

Ray bundle 205 provides a sub-eyebox 220 from which eye 155 can perceive display pixel 215 while ray bundle 210 provides another sub-eyebox 225 from which eye 155 can perceive display pixel 215. The sub-eyeboxes 220 and 225 are seamlessly stitched together to form an extended eyebox 215. This stitching of ray bundles 205 and 210 to extend eyebox 220 is achieved by configuring the curvatures of input coupler 115, output coupler 125, eye-ward facing surface 135, and world facing surface 140.

Conventionally, ray bundles from a single display pixel that encounter a different number of reflections within a lightguide of an eyepiece would result in a deleterious ghost image that is disjoint from the primary image. As such, conventional optical designers strive to prevent, block, or otherwise dispose of the ghost image before it reaches eye 155. However, the design of eyepiece 100 seeks to leverage these dual path reflections by seamlessly stitching them together at the output of eyepeice 100 to form a larger, extended eyebox 215.

FIGS. 3A and 3B illustrate a monocular head wearable display 300 using an eyepiece 301, in accordance with an embodiment of the disclosure. FIG. 3A is a perspective view of head wearable display 300, while FIG. 3B is a top view of the same. Eyepiece 301 may be implemented with embodiments of eyepiece 100 as discussed above, or any of the other eyepiece embodiments described below (or combinations thereof). Eyepiece 301 is mounted to a frame assembly, which includes a nose bridge 305, left ear arm 310, and right ear arm 315. Housings 320 and 225 may contain various electronics including a microprocessor, interfaces, one or more wireless transceivers, a battery, a camera, a speaker, a display source, etc. Although FIGS. 3A and 3B illustrate a monocular embodiment, head wearable display 300 may also be implemented as a binocular display with two eyepieces 301 each aligned with a respective eye of the user when display 300 is worn.

The see-through eyepiece 301 is secured into an eye glass arrangement so head wearable display can be worn on the head of a user. The left and right ear arms 310 and 315 rest over the user's ears while nose bridge 305 rests over the user's nose. The frame assembly is shaped and sized to position viewing region 130 in front of an eye of the user. Other frame assemblies having other shapes may be used (e.g., traditional eyeglasses frame, a single contiguous headset member, a headband, goggles type eyewear, etc.).

As mentioned, FIGS. 3A and 3B illustrate a monocular embodiment with a compact see-through eyepiece that only covers a portion of the user's field of view. In other embodiments, the eye-ward facing and world facing surfaces of the see-through eyepiece can be extended to form full eyeglass lenses in a binocular frame. FIG. 4 illustrates a binocular head wearable display 400 including two see-through eyepieces 401 integrated into a frame and which eyepieces extend across a substantial portion of the user's field of view. The see-through add-on component (e.g., see-through add-on component 110 in FIG. 1) of each eyepiece 401 may be designed to extend across the entire eyepiece so that no seam is formed in the middle portion of the eyepiece. Display light 145 may be launched into eyepieces 401 at the peripheral temple regions and guided towards out couplers 125 via TIR, as described above. These full eyeglass lenses may be implemented with or without prescription curvatures of the outside surfaces.

FIG. 5 illustrates an example see-through add-on component 501 that extends across the entire eyepiece 500 to avoid surface seams in the central region of the eyepiece, in accordance with an embodiment of the disclosure. The illustrated embodiment of eyepiece 500 includes a curved lightguide component 505, see-through add-on component 501, input coupler 510, and output coupler 515. The illustrated embodiment of curved lightguide component 505 includes a thick portion 520 and a thin portion 525. The illustrated embodiment of see-through add-on component 501 includes a thick portion 530 and a thin portion 535.

Eyepiece 500 is similar to eyepiece 100 and operates in a similar manner, except that the thin portion 535 of see-through add-on component 501 conformably mates to and extends across the world side of thick portion 520 of curved lightguide component 505. Similarly, the thin portion 525 of curved lightguide component 505 conformably mates to and extends across the eye-ward side of thick portion 530 of see-through add-on component 501. Output coupler 515 is disposed at the transitions between the thin and thick portions. The thin portions 525 and 535 provide continuous outside surfaces without seams, thereby improving the industrial design.

In one embodiment, see-through add-on component 501 is bonded to curved lightguide component 505 using a low refractive index glue (lower than the refractive index of curved lightguide component 505 and see-through add-on component 501) to preserve TIR at the interface boundary. Thin portions 525 and 535 may be fabricated by grinding or sanding the surfaces of see-through add-on component 501 and curved lightguide component 505 to achieve the desired thickness after bonding the two components together.

The illustrated embodiment of head wearable displays 300 or 400 are capable of displaying an augmented reality to the user. Eyepieces 301, 401, or 500 permit the user to see a real world image via ambient light 185. Left and right display images (binocular embodiment illustrated in FIG. 4) may be generated by display sources 150 mounted in peripheral corners outside the user's central vision. Display light 145 is seen by the user as a virtual image superimposed over ambient light 185 as an augmented reality. As mentioned above, in some embodiments, the outer surfaces of these eyepieces may not have complementary curvatures to impart prescriptive correction on ambient light 185.

FIGS. 6A-6D illustrate various alternative examples of input couplers and output couplers that can be used in connection with the eyepiece designs (e.g., eyepieces 100, 301, 401, or 500) described above, in accordance with embodiments of the disclosure.

For example, FIG. 6A illustrates an eyepiece 605 where an input coupler 610 is formed as an input surface molded into an end of curved waveguide component 615. In other words, the display light 145 is not input through the eye-ward facing surface, but rather, through an end surface proximate to display source 150.

FIG. 6B illustrates an eyepiece 620 where the output coupler is formed as an array of prism structures 625 disposed along the world facing surface 630 in the viewing region. Prism structures 625 may be implemented as an array of small obliquely angled partially reflective surfaces. In the illustrated embodiment of FIG. 6B, a plurality of see-through add-on components 635 are bonded to curved waveguide component 640 behind each reflective surface. Although not illustrated, in some embodiments, eyepiece 620 may further include an array of prism structures as an input coupler in the input region. Using prism structures at the input region can compensate for lateral chromatic aberrations induced by the output prism structures 625.

FIG. 6C illustrates an eyepiece 650 where the output coupler is formed as a hologram 655 disposed along the world facing surface 660 in the viewing region. In this embodiment, a see-through add-on component may be omitted. Furthermore, FIG. 6C illustrates the inclusion of a reflective hologram 657 as an input coupler to provide color correction for chromatic aberrations induced by the output hologram 655.

FIG. 6D illustrates an eyepiece 670 where the output coupler is formed as a pair of partially reflective mirror segments 675 and 680 disposed within curved waveguide component 685. Partially reflective mirror segments 675 and 680 operate to further expand the eyebox from which display light 145 can be viewed from eyepiece 670. In other words, mirror segments 675 and 680 reflect display light output from a single pixel in a manner that stitches the images reflected by each minor segment 675 and 680 together at the viewing region to extend the eyebox from which the single pixel can be viewed. Partially reflective mirror segment 680 is disposed behind partially reflective minor segment 675 such that display light 145 must first pass through partially reflective minor segment 675 before reaching partially reflective mirror segment 680. In the illustrated embodiment, partially reflective mirror segments 675 and 680 are both curved freeform surfaces while world facing surface 690 and eye-ward facing surface 695 are spherical surfaces. In one embodiment, world facing surface 690 is a sphere with a radius of 90 mm and eye-ward facing surface 695 is a sphere with a radius of 92.5 mm. In one embodiment, partially reflective minor segment 675 has a freeform shape defined by equations 1 and 2 with coefficient values of x²=0.0035, y²=0.00453, with a relative tilt of 23.25 degrees; partially reflective minor segment 680 has a freeform shape defined by equations 1 and 2 with coefficient values of x²=0.00457, y²=0.00525, with a relative tilt of 26 degrees; and input coupler 697 has a freeform shape defined by equations 1 and 2 with coefficient values of x²=−0.0053, y²=−0.00273, x³=7.142E-005, x²y=−6.076E-006, xy²=5.2072E-005, (x,y,z)=(−28.5, 0, −3) with a relative tilt of 48.8 degrees. Of course, other coefficient values and dimensions may be implemented.

The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation. 

What is claimed is:
 1. An eyepiece for a head wearable display, the eyepiece comprising: a curved lightguide component for guiding display light received at an input region peripherally located from a viewing region and emitting the display light along an eye-ward direction in the viewing region, the curved lightguide component including: an eye-ward facing surface that is concave; and a world facing surface that is convex and opposite the eye-ward facing surface; an input coupler disposed at the input region to couple the display light into the curved lightguide component; and an output coupler disposed at the viewing region to redirect the display light towards the eye-ward direction for output from the curved lightguide component, wherein the output coupler is partially transmissive to ambient light incident through the world facing surface such that the viewing region is see-through, wherein the display light is guided between the input coupler and the output coupler entirely by total internal reflection.
 2. The eyepiece of claim 1, wherein the input coupler and the output coupler are configured to redirect light rays of the display light received from a single pixel of a display source along one of two different paths through the curved lightguide component such that a first group of the light rays encounters a different number of total internal reflections than a second group of the light rays.
 3. The eyepiece of claim 2, wherein the first group of the light rays and the second group of the light rays stitch together at the viewing region to extend an eyebox from which the single pixel can be viewed.
 4. The eyepiece of claim 1, wherein in the input coupler comprises a mirror having a first freeform surface and wherein the display light enters into the curved lightguide component through the eye-ward facing surface.
 5. The eyepiece of claim 1, wherein the output coupler comprises a beam splitter having a second freeform surface, wherein the beam splitter is more transmissive than reflective to visible light.
 6. The eyepiece of claim 5, further comprising a see-through add-on component disposed across the viewing region with the output coupler disposed along an interface between the see-through add-on component and the curved lightguide component, wherein the see-through add-on component and the curved lightguide component have a substantially same refractive index.
 7. The eyepiece of claim 6, wherein the see-through add-on component has a thin portion and a thick portion and the curved lightguide component has a thin portion and a thick portion, wherein the thin portion of the see-through add-on component conformably mates to the thick portion of the curved waveguide component and wherein the thin portion of the curved waveguide component conformably mates to the thick portion of the see-through add-on component, wherein the output coupler is disposed at a transition from the thick portions to the thin portions of the see-through add-on component and the curved waveguide component.
 8. The eyepiece of claim 1, wherein input coupler comprises an input surface molded into an end surface of the curved waveguide component that is not the eye-ward facing surface.
 9. The eyepiece of claim 1, wherein the output coupler comprises array of prism structures disposed along the world facing surface.
 10. The eyepiece of claim 1, wherein the output coupler comprises a hologram disposed along the world facing surface.
 11. The eyepiece of claim 1, wherein the output coupler comprises first and second partial reflective minor segments disposed within the curved waveguide component to expand an eyebox of the display light, wherein the second partial reflective minor segment is disposed behind the first partial reflective minor segment such that the display light must pass through the first partial reflective mirror segment before reaching the second partial reflective minor segment.
 12. The eyepiece of claim 11, wherein the first and second partial reflective minor segments are curved freeform surfaces.
 13. The eyepiece of claim 1, wherein the eye-ward facing surface and the world facing surface of the curved lightguide component are both spherical surfaces.
 14. A head wearable display, comprising: a display source to generate display light at a peripheral location; a curved lightguide component for guiding the display light to a viewing region offset from the peripheral location and emitting the display light along an eye-ward direction in the viewing region, the curved lightguide component including: an eye-ward facing surface that is concave; and a world facing surface that is convex and opposite the eye-ward facing surface; an input coupler disposed at the input region to couple the display light into the curved lightguide component; an output coupler disposed at the viewing region to redirect the display light towards the eye-ward direction for output from the curved lightguide component, wherein the output coupler is partially transmissive to ambient light incident through the world facing surface such that the viewing region is see-through, wherein the display light is guided between the input coupler and the output coupler entirely by total internal reflection; and a frame assembly to support the curved lightguide component and the display source for wearing on a head of a user with the viewing region positioned in front of an eye of the user.
 15. The head wearable display of claim 14, wherein the input coupler and the output coupler are configured to redirect light rays of the display light received from a single pixel of a display source along one of two different paths through the curved lightguide component such that a first group of the light rays encounters a different number of total internal reflections than a second group of the light rays.
 16. The head wearable display of claim 15, wherein the first group of the light rays and the second group of the light rays stitch together at the viewing region to extend an eyebox from which the single pixel can be viewed.
 17. The head wearable display of claim 14, wherein in the input coupler comprises a mirror having a first freeform surface and wherein the display light enters into the curved lightguide component through the eye-ward facing surface.
 18. The head wearable display of claim 14, wherein the output coupler comprises a beam splitter having a second freeform surface, wherein the beam splitter is more transmissive than reflective to visible light.
 19. The head wearable display of claim 18, further comprising a see-through add-on component disposed across the viewing region with the output coupler disposed along an interface between the see-through add-on component and the curved lightguide component, wherein the see-through add-on component and the curved lightguide component have a substantially same refractive index.
 20. The head wearable display of claim 14, wherein input coupler comprises an input surface molded into an end surface of the curved waveguide component that is not the eye-ward facing surface.
 21. The head wearable display of claim 14, wherein the output coupler comprises either one of an array of prism structures disposed along the world facing surface or a hologram disposed along the world facing surface.
 22. The head wearable display of claim 14, wherein the output coupler comprises first and second partial reflective minor segments disposed within the curved waveguide component to expand an eyebox of the display light, wherein the second partial reflective mirror segment is disposed behind the first partial reflective minor segment such that the display light must pass through the first partial reflective mirror segment before reaching the second partial reflective minor segment.
 23. The head wearable display of claim 22, wherein the first and second partial reflective minor segments are curved freeform surfaces.
 24. The head wearable display of claim 14, further comprising: an infrared camera to monitor eye movements using infrared light; and an optical combiner disposed adjacent to the input region, the optical combiner to combine the display light and the infrared light for propagation along a common path through the curved lightguide component. 